Driving POWER LEDs ...

3A ... of constant current on about 100W ... i could drive a lot of LEDs with this !
If i drive 5 similars rails of LEDs, i could expect approx 600mA of current, which is good for me. (i could optimize their lastlife).

What do you think of this ?

You seem to miss the concept and need that each LED needs constantly controlled 700ma of current. How is the 3 amp constant current power source you linked to able to partial out constant 700ma current paths to each specific led?

Lefty